The laying of flexible tubular conduits subsea is usually preformed from a suitable pipe-laying/pipelay vessel such as a floating platform, barge, ship or other vessel. The flexibly tubular conduit may be one of many different forms. The flexible tubular conduit is preferably a flexible pipe of the unbounded type for conveying hydrocarbons as defined in the American Petroleum Institute Recommendations API17J “Specification for unbounded flexible tubular conduit”. However, the flexible tubular conduit may be of the bonded type. The flexible tubular conduit may alternatively be an umbilical as defined in the American Petroleum Institute API17E “Specification for subsea umbilical” third Edition, 2003. Alternatively, the flexible tubular conduit may be an Integrated Production Bundle (IPB) described in the U.S. Pat. No. 6,102,077 and marketed by the applicant under the registered trademark ISU® (Integrated Subsea Umbilical).
The flexible tubular conduit is stored in a basket or on a reel on the deck of the vessel and in one method is fed from the basket/reel to a vertical pipelay tower, where it is vertically aligned prior to laying the flexible tubular conduit underwater.
Guiding means in the form of an aligner, chute or a reel is positioned on the top of the pipelay tower and used to divert the flexible tubular conduit from a horizontal path to a vertical path for laying. The guiding means generally comprises a groove, channel or gutter for receiving the flexible tubular conduit and for facilitating the diverting of the flexible tubular conduit from the horizontal path to the vertical path.
The pipelay tower further comprises tensioning means, for example pipe tensioners comprising one or more caterpillar tracks, to facilitate the feeding of the flexible tubular conduit along the required vertical path. In use, the tensioning means grip the flexible tubular conduit and help feed and deploy the flexible tubular conduit towards the seabed.
A flexible tubular conduit is generally provided with one or more fittings, such as an end fitting and/or stiffener, which generally have an outer diameter that is greater than the outer diameter of the flexible tubular conduit.
Where a fitting is provided at the second end of the flexible tubular conduit, i.e. the terminal end of the flexible tubular conduit, the fitting will need to be lowered past the tensioning means for deployment subsea without the aid of the tensioning means.
GB2303897 describes a device for laying flexible conduits from a floating support. The device comprises a primary tensioning means, of the linear hoisting type to provide for the normal lowering of the flexible conduit, and a secondary tensioning means to provide for the lowering of the flexible conduit when the accessory has passed the primary tensioning means. The secondary tensioning means comprises at least one elongate movable handling member actuated by motor means in order to displace it vertically, and connected at one end to a clamp intended to be tightened around the flexible conduit.